Self-regulation and cross-regulation of pattern-recognition receptor signalling in health and disease

Neddylation Facilitates the Antiviral Response in Zebrafish

Neddylation is a type of post-translational protein modifications, in which neural precursor cell expressed developmentally downregulated protein 8 (NEDD8) is covalently conjugated to the lysine residues of target substrates. The best characterized principal substrates of neddylation are the cullin-RING ligases (CRLs). In addition, neddylation also modifies non-cullin proteins to affect gene regulation, cell survival, organ development, and stress response. However, the role of neddylation in antiviral innate immunity remain largely unknown. Here, we found that when neddylation was blocked by the NEDD8 activating enzyme E1 (NAE) inhibitor, MLN4924, the cellular and organismal antiviral response was suppressed. Moreover, the disruption of nedd8 increased the sensitivity of zebrafish to SVCV infection. Further assays indicated that blocking or silencing neddylation significantly downregulated key antiviral genes after poly (I:C) stimulation or SVCV infection, but dramatically increased SVCV replication. Neddylation of Irf3 and Irf7 was readily detected, but not of Mda5, Mavs, and Tbk1. Thus, our results not only demonstrated that neddylation facilitated the antiviral response in vitro and in vivo, but also revealed a novel role of nedd8 in antiviral innate immunity.

Interferon-inducible cytoplasmic lncLrrc55-AS promotes antiviral innate responses by strengthening IRF3 phosphorylation

Type I interferon (IFN-I) production is efficiently induced to ensure a potent innate immune response to viral infection. How this response can be enhanced, however, remains to be explored. Here, we identify a new cytoplasmic long non-coding RNA (lncRNA), lncLrrc55-AS, that drives a positive feedback loop to promote interferon regulatory factor 3 (IRF3) signaling and IFN-I production. We show that lncLrrc55-AS is virus-induced in multiple cell types via the IFN-JAK-STAT pathway. LncLrrc55-AS-deficient mice display a weakened antiviral immune response and are more susceptible to viral challenge. Mechanistically, lncLrrc55-AS binds phosphatase methylesterase 1 (PME-1), and promotes the interaction between PME-1 and the phosphatase PP2A, an inhibitor of IRF3 signaling. LncLrrc55-AS supports PME-1-mediated demethylation and inactivation of PP2A, thereby enhancing IRF3 phosphorylation and signaling. Loss of PME-1 phenocopies lncLrrc55-AS deficiency, leading to diminished IRF3 phosphorylation and IFN-I production. We have identified an IFN-induced lncRNA as a positive regulator of IFN-I production, adding mechanistic insight into lncRNA-mediated regulation of signaling in innate immunity and inflammation.

An endosomal LAPF is required for macrophage endocytosis and elimination of bacteria

Macrophages can internalize the invading pathogens by raft/caveolae and/or clathrin-dependent endocytosis and elicit an immune response against infection. However, the molecular mechanism for macrophage endocytosis remains elusive. Here we report that LAPF (lysosome-associated and apoptosis-inducing protein containing PH and FYVE domains) is required for caveolae-mediated endocytosis. Lapf -deficient macrophages have impaired capacity to endocytose and eliminate bacteria. Macrophage-specific Lapf-deficient mice are more susceptible to Escherichia coli (E. coli) infection with higher bacterial loads. Moreover, Lapf deficiency impairs TLR4 endocytosis, resulting in attenuated production of TLR-triggered proinflammatory cytokines. LAPF is localized to early endosomes and interacts with caveolin-1. Phosphorylation of LAPF by the tyrosine kinase Src is required for LAPF-Src-Caveolin complex formation and endocytosis and elimination of bacteria. Collectively, our work demonstrates that LAPF is critical for endocytosis of bacteria and induction of inflammatory responses, suggesting that LAPF and Src could be potential targets for the control of infectious diseases.

Development and characterization of a stable bovine intestinal sub-epithelial myofibroblast cell line from ileum of a young calf

Intestinal sub-epithelial myofibroblasts (ISEMFs) are mesenchymal cells that do not express cytokeratin but express α-smooth muscle actin and vimentin. Despite being cells with diverse functions, there is a paucity of knowledge about their origin and functions primarily due to the absence of a stable cell line. Although myofibroblast in vitro models for human, mouse, and pig are available, there is no ISEMF cell line available from young calves. We isolated and developed an ileal ISEMF cell line from a 2-d-old calf that expressed α-smooth muscle actin and vimentin but no cytokeratin indicating true myofibroblast cells. To overcome replicative senescence, we immortalized primary cells with SV40 large T antigen. We characterized and compared both primary and immortalized ileal ISEMF cells for surface glycan and Toll-like-receptor (TLR) expression by lectin-binding assay and real-time quantitative PCR (RT-qPCR) assay respectively. SV40 immortalization significantly decreased surface lectin binding for lectins GSL-I, PHA-L, ECL, Jacalin, Con-A, LCA, and LEL. Both cell types expressed TLRs 1-9 and showed no significant differences in TLR expression. Thus, these cells can be useful in vitro model to study ISEMF's origin, physiology, and functions.

TLR1/2 Specific Small-Molecule Agonist Suppresses Leukemia Cancer Cell Growth by Stimulating Cytotoxic T Lymphocytes

Toll-like receptor 2 (TLR2) expressed on antigen presenting cells evokes a series of critical cytokines, which favor the development of tumor-specific cytotoxic T lymphocytes (CTLs). Therefore, TLR2 represents an attractive cancer immunotherapeutic target. Here, a synthetic library of 14 000 compounds together with a series of newly developed compounds for NF-κB activation using HEK-Blue hTLR2 cells is initially screened. Following further screening in a variety of cells including HEK-Blue hTLRs reporter cells, murine, and human macrophage cell lines, a potent small molecule agonist 23 (SMU-Z1) is identified, which specifically activates TLR2 through its association with TLR1, with a EC50 of 4.88 ± 0.79 × 10-9 m. Toxicology studies, proinflammatory cytokines (e.g., TNF-α, IL-1β, IL-6, and nitric oxide) and target-protein based biophysical assays demonstrate the pharmacologically relevant characteristics of SMU-Z1. In addition, SMU-Z1 promotes murine splenocyte proliferation and upregulates the expression of CD8+ T cells, NK cells and DCs, which results in a significant antitumor effect in a murine leukemia model. Finally, the induced tumors in three out of seven mice disappear after administration of SMU-Z1. Our studies thus identify a novel and potent TLR1/2 small molecule agonist, which displays promising immune adjuvant properties and antitumor immunity.

E3 ubiquitin ligase RNF170 inhibits innate immune responses by targeting and degrading TLR3 in murine cells

Upon recognition of dsRNA, toll-like receptor 3 (TLR3) recruits the adaptor protein TRIF to activate IRF3 and NF-κB signaling, initiating innate immune responses. The ubiquitination of TLR3 downstream signaling molecules and their roles in the innate response have been discovered; however, whether TLR3 itself is ubiquitinated and then functionally involved remains to be elucidated. By immunoprecipitating TLR3-binding proteins in macrophages, we identified ring finger protein 170 (RNF170) as a TLR3-binding E3 ligase. RNF170 mediated the K48-linked polyubiquitination of K766 in the TIR domain of TLR3 and promoted the degradation of TLR3 through the proteasome pathway. The genetic ablation of RNF170 selectively augmented TLR3-triggered innate immune responses both in vitro and in vivo. Our results reveal a novel role for RNF170 in selectively inhibiting TLR3-triggered innate immune responses by promoting TLR3 degradation.

KAT8 selectively inhibits antiviral immunity by acetylating IRF3

Optimal activation of IRF3 is crucial for maintaining immune homeostasis. Huai et al. demonstrate that KAT8 acetylates IRF3 at lysine 359, inhibits IRF3 recruitment to promoters of type I interferon genes, and then decreases type I interferon production to attenuate antiviral innate immune responses.

The transcription factor interferon regulatory factor 3 (IRF3) is essential for virus infection–triggered induction of type I interferons (IFN-I) and innate immune responses. IRF3 activity is tightly regulated by conventional posttranslational modifications (PTMs) such as phosphorylation and ubiquitination. Here, we identify an unconventional PTM of IRF3 that directly inhibits its transcriptional activity and attenuates antiviral immune response. We performed an RNA interference screen and found that lysine acetyltransferase 8 (KAT8), which is ubiquitously expressed in immune cells (particularly in macrophages), selectively inhibits RNA and DNA virus–triggered IFN-I production in macrophages and dendritic cells. KAT8 deficiency protects mice from viral challenge by enhancing IFN-I production. Mechanistically, KAT8 directly interacts with IRF3 and mediates IRF3 acetylation at lysine 359 via its MYST domain. KAT8 inhibits IRF3 recruitment to IFN-I gene promoters and decreases the transcriptional activity of IRF3. Our study reveals a critical role for KAT8 and IRF3 lysine acetylation in the suppression of antiviral innate immunity.

E3 ubiquitin ligase Nedd4 is a key negative regulator for non-canonical inflammasome activation

The non-canonical inflammasome plays important roles in endotoxic shock and pyroptosis. Murine caspase-11, corresponding to human caspase-4, is centrally located in the non-canonical inflammasome pathway, which is directly activated by cytosolic lipopolysaccharide. It has been reported that ubiquitination strictly regulates inflammatory responses. However, the role of ubiquitination in regulating the non-canonical inflammasome is little known. In this study, we show that the E3 ubiquitin ligase, Nedd4 is an important negative regulatory component of the non-canonical inflammasome pathway. Nedd4 deficiency promoted mouse death from sepsis and cell pyroptosis, resulting from non-canonical inflammasome activation. Furthermore, Nedd4 induced the K48-linked polyubiquitination and subsequent degradation of caspase-11 through the 26S proteasome. Meanwhile, caspase-11 (or caspase-4) reciprocally regulated the level of Nedd4 protein by cleavage. Thus, Nedd4 appears to have a key role in balancing the level of non-canonical inflammasome activation in response to gram-negative bacterial infection.

Transcriptional profiling of macrophages infected with Fonsecaea monophora

Fonsecaea monophora is a member of dematiaceous fungi capable of causing chromoblastomycosis through traumatic injury. However, little is known about the pathogenesis and early interactions between F. monophora and host. The aim of this study was to explore the potential mechanism of macrophages against F. monophora, especially the role of melanin during the pathogenic process. We carried out RNA sequencing based on the Illumina system. It showed that according to melanin contents, different strains of F. monophora induced different transcriptional profilings in macrophages. Functional analyses suggested the biological functions of differentially expressed genes were closely related to immune response, and the melanin might affect the interactions by regulating the MAPK signalling pathway of macrophages. Our results provide insights into the pathogenesis of infection by F. monophora conidia.

β-1,3-Glucan/CR3/SYK pathway-dependent LC3B-II accumulation enhanced the fungicidal activity in human neutrophils

Since molecular genotyping has been established for the Candida species, studies have found that a single Candida strain (endemic strain) can persist over a long period of time and results in the spread of nosocomial invasive candidiasis without general characteristics of horizontal transmissions. Our previous study also found the existence of endemic strains in a cancer center in Tianjin, China. In the current study, we performed further investigation on endemic and non-endemic Candida albicans strains, with the aim of explaining the higher morbidity of endemic strains. In an in vivo experiment, mice infected with endemic strains showed significantly shorter survival time and higher kidney fungal burdens compared to mice infected with non-endemic strains. In an in vitro experiment, the killing percentage of neutrophils to endemic strains was significantly lower than that to non-endemic strains, which is positively linked to the ratio of LC3B-II/I in neutrophils. An immunofluorescence assay showed more β-1,3-glucan exposure on the cell walls of non-endemic strains compared to endemic strains. After blocking the β-glucan receptor (CR3) or inhibiting downstream kinase (SYK) in neutrophils, the killing percent to C. albicans (regardless of endemic and non-endemic strains) and the ratio of LC3B-II/I of neutrophils were significantly decreased. These data suggested that the killing capability of neutrophils to C. albicans was monitored by β-1,3-glucan via CR3/SYK pathway-dependent LC3B-II accumulation and provided an explanation for the variable killing capability of neutrophils to different strains of C. albicans, which would be beneficial in improving infection control and therapeutic strategies for invasive candidiasis.

Crosstalk between Autophagy and Type I Interferon Responses in Innate Antiviral Immunity

Autophagy exhibits dual effects during viral infections, promoting the clearance of viral components and activating the immune system to produce antiviral cytokines. However, some viruses impair immune defenses by collaborating with autophagy. Mounting evidence suggests that the interaction between autophagy and innate immunity is critical to understanding the contradictory roles of autophagy. Type I interferon (IFN-I) is a crucial antiviral factor, and studies have indicated that autophagy affects IFN-I responses by regulating IFN-I and its receptors expression. Similarly, IFN-I and interferon-stimulated gene (ISG) products can harness autophagy to regulate antiviral immunity. Crosstalk between autophagy and IFN-I responses could be a vital aspect of the molecular mechanisms involving autophagy in innate antiviral immunity. This review briefly summarizes the approaches by which autophagy regulates antiviral IFN-I responses and highlights the recent advances on the mechanisms by which IFN-I and ISG products employ autophagy against viruses.

Delivery of 5'-triphosphate RNA with endosomolytic nanoparticles potently activates RIG-I to improve cancer immunotherapy

RNA agonists of the retinoic acid gene I (RIG-I) pathway have recently emerged as a promising class of cancer immunotherapeutics, but their efficacy is hindered by drug delivery barriers, including nuclease degradation, poor intracellular uptake, and minimal access to the cytosol where RIG-I is localized. Here, we explore the application of pH-responsive, endosomolytic polymer nanoparticles (NPs) to enhance the cytosolic delivery and immunostimulatory activity of synthetic 5' triphosphate, short, double-stranded RNA (3pRNA), a ligand for RIG-I. Delivery of 3pRNA with pH-responsive NPs with an active endosomal escape mechanism, but not control carriers lacking endosomolytic activity, significantly increased the activity of 3pRNA in dendritic cells, macrophages, and cancer cell lines. In a CT26 colon cancer model, activation of RIG-I via NP delivery of 3pRNA induced immunogenic cell death, triggered expression of type I interferon and pro-inflammatory cytokines, and increased CD8+ T cell infiltration into the tumor microenvironment. Consequently, intratumoral (IT) delivery of NPs loaded with 3pRNA inhibited CT26 tumor growth and enhanced the therapeutic efficacy of anti-PD-1 immune checkpoint blockade, resulting in a 30% complete response rate and generation of immunological memory that protected against tumor rechallenge. Collectively, these studies demonstrate that pH-responsive NPs can be harnessed to strongly enhance the immunostimulatory activity and therapeutic efficacy of 3pRNA and establish endosomal escape as a critical parameter in the design of carriers for immunotherapeutic targeting of the RIG-I pathway.

Mucosal Vaccine Approaches for Prevention of HIV and SIV Transmission

Optimal protective immunity to HIV will likely require that plasma cells, memory B cells and memory T cells be stationed in mucosal tissues at portals of viral entry. Mucosal vaccine administration is more effective than parenteral vaccine delivery for this purpose. The challenge has been to achieve efficient vaccine uptake at mucosal surfaces, and to identify safe and effective adjuvants, especially for mucosally administered HIV envelope protein immunogens. Here, we discuss strategies used to deliver potential HIV vaccine candidates in the intestine, respiratory tract, and male and female genital tract of humans and nonhuman primates. We also review mucosal adjuvants, including Toll-like receptor agonists, which may adjuvant both mucosal humoral and cellular immune responses to HIV protein immunogens.

Western Diet Triggers NLRP3-Dependent Innate Immune Reprogramming

Long-term epigenetic reprogramming of innate immune cells in response to microbes, also termed "trained immunity," causes prolonged altered cellular functionality to protect from secondary infections. Here, we investigated whether sterile triggers of inflammation induce trained immunity and thereby influence innate immune responses. Western diet (WD) feeding of Ldlr^-/- mice induced systemic inflammation, which was undetectable in serum soon after mice were shifted back to a chow diet (CD). In contrast, myeloid cell responses toward innate stimuli remained broadly augmented. WD-induced transcriptomic and epigenomic reprogramming of myeloid progenitor cells led to increased proliferation and enhanced innate immune responses. Quantitative trait locus (QTL) analysis in human monocytes trained with oxidized low-density lipoprotein (oxLDL) and stimulated with lipopolysaccharide (LPS) suggested inflammasome-mediated trained immunity. Consistently, Nlrp3^-/-/Ldlr^-/- mice lacked WD-induced systemic inflammation, myeloid progenitor proliferation, and reprogramming. Hence, NLRP3 mediates trained immunity following WD and could thereby mediate the potentially deleterious effects of trained immunity in inflammatory diseases.

Transcriptome analysis of Aeromonas hydrophila infected hybrid sturgeon (Huso dauricus×Acipenser schrenckii)

The hybrid sturgeon (Huso dauricus × Acipenser schrenckii) is an economically important species in China. With the increasing aquaculture of hybrid sturgeon, the bacterial diseases are a great concern of the industry. In this study, de novo sequencing was used to compare the difference in transcriptome in spleen of the infected and mock infected sturgeon with Aeromonas hydrophila. Among 187,244 unigenes obtained, 87,887 unigenes were annotated and 1,147 unigenes were associated with immune responses genes. Comparative expression analysis indicated that 2,723 differently expressed genes between the infected and mock-infected group were identified, including 1,420 up-regulated and 1,303 down-regulated genes. 283 differently expressed anti-bacterial immune related genes were scrutinized, including 168 up-regulated and 115 down-regulated genes. Ten of the differently expressed genes were further validated by qRT-PCR. In this study, toll like receptors (TLRs) pathway, NF-kappa B pathway, class A scavenger receptor pathway, phagocytosis pathway, mannose receptor pathway and complement pathway were shown to be up-regulated in Aeromonas hydrophila infected hybrid sturgeon. Additionally, 65,040 potential SSRs and 2,133,505 candidate SNPs were identified from the hybrid sturgeon spleen transcriptome. This study could provide an insight of host immune genes associated with bacterial infection in hybrid sturgeon.

Radiation, Immune Checkpoint Blockade and the Abscopal Effect: A Critical Review on Timing, Dose and Fractionation

The combination of radiation and immunotherapy is currently an exciting avenue of pre-clinical and clinical investigation. The synergy between these two treatment modalities has the potential to expand the role of radiation from a purely local therapy, to a role in advanced and metastatic disease. Tumor regression outside of the irradiated field, known as the abscopal effect, is a recognized phenomenon mediated by lymphocytes and enhanced by checkpoint blockade. In this review, we summarize the known mechanistic data behind the immunostimulatory effects of radiation and how this is enhanced by immunotherapy. We also provide pre-clinical data supporting specific radiation timing and optimal dose/fractionation for induction of a robust anti-tumor immune response with or without checkpoint blockade. Importantly, these data are placed in a larger context of understanding T-cell exhaustion and the impact of immunotherapy on this phenotype. We also include relevant pre-clinical studies done in non-tumor systems. We discuss the published clinical trials and briefly summarize salient case reports evaluating the abscopal effect. Much of the data discussed here remains at the preliminary stage, and a number of interesting avenues of research remain under investigation.

Glycolipid iGb3 feedback amplifies innate immune responses via CD1d reverse signaling

The cross-talk between cellular lipid metabolism and the innate immune responses remains obscure. In addition to presenting lipid antigens to Natural Killer T-cells (NKT cells), the Cluster of Differentiation 1D Glycoprotein (CD1d) might mediate reverse signaling in antigen-presenting cells (APCs). Here we found CD1d deficiency attenuated Toll-like receptor (TLR)-triggered inflammatory innate responses in macrophages and dendritic cells, protecting mice from endotoxin shock. TLR activation in macrophages induced metabolic changes of glycosphingolipids (GSLs), among which glycolipid isoglobotrihexosylceramide (iGb3) was rapidly produced. The endogenously generated iGb3 bound CD1d in endosomal compartments and then synergized with the initially activated TLR signal to induce Tyr332 phosphorylation of CD1d intracellular domain. This led to the recruitment and activation of proline-rich tyrosine kinase 2 (Pyk2). Pyk2 interacted with IκB kinase β (IKKβ) and TANK-binding kinase 1 (TBK1), and enhanced tyrosine phosphorylation of Tyr188/199 of IKKβ and Tyr179 of TBK1 and thus, their activation to promote full activation of TLR signaling. Thus, intracellular CD1d reverse signaling, triggered by endogenous iGb3, amplifies inflammatory innate responses in APCs. Our findings identify a non-canonical function of CD1d reverse signaling activated by lipid metabolite in the innate immune response.

Overexpression of Toll-like receptor 4 enhances LPS-induced inflammatory response and inhibits Salmonella Typhimurium growth in ovine macrophages

The Toll-like receptor 4 (TLR4) plays a crucial role in innate inflammatory responses, as it recognizes gram-negative bacteria (or their products) and contributes greatly to host defense against invading pathogens. Though TLR4 overexpressing transgenic sheep, resistant to certain diseases related with gram-negative bacteria, had been bred in our previous research, the effects of overexpression of TLR4 on innate immune response remained unclear. In this study, TLR4 overexpressing ovine macrophages were obtained from peripheral blood, and it was found that the overexpression of TLR4 initially promoted the production of proinflammatory cytokines TNFα and IL-6 by activating TLR4-mediated IRAK4-dependent NF-κB and MAPK (JNK and ERK1/2) signaling following LPS stimulation. However, this effect was later impaired due to increased internalization of TLR4 into endosomal compartment of the macrophages. Then the overexpression of TLR4 triggered TBK1-dependent interferon-regulatory factor-3 (IRF-3) expression, which in turn led to the induction of IFN-β and IFN-inducible genes (i.e.IP10, IRG1 and GARG16). Understandably, an increased IFN-β level facilitated phosphorylation of STAT1 to induce expression of innate antiviral genes Mx1 and ISG15, suggesting that TLR4 overexpressing macrophages were equipped better against viral infection. Correspondingly, the bacterial burden in these macrophages, after infection with live S. Typhimurium, was decreased significantly. In summary, the results indicated that overexpression of TLR4 could enhance innate inflammatory responses, initiate the innate antiviral immunity, and control effectively S. Typhimurium growth in ovine macrophages.

A Novel Lipopolysaccharide Recognition Mechanism Mediated by Internalization in Teleost Macrophages

Macrophages in teleosts are less sensitive to lipopolysaccharide (LPS) compared to mammals. The functional equivalent of the mammalian LPS surface receptor in teleost macrophages for the pro-inflammatory response is either non-existent or replaced by negative regulation. LPS signaling in teleost macrophages remains unclear. Here, we found a scavenger receptor class B 2a (PaSRB2a) that played a crucial role in LPS signaling in teleost macrophages. The internalization of LPS and subsequent pro-inflammatory responses in macrophages were mediated by PaSRB2a, which is a novel isoform of the mammalian SRB2 gene. LPS internalization by PaSRB2a is dependent on its C-terminal intracellular domain. Following LPS internalization, it interacts with the ayu intracellular receptors nucleotide-binding oligomerization domain protein 1 (PaNOD1) and PaNOD2. Moreover, LPS pre-stimulation with sub-threshold concentrations reduced the effect of secondary LPS treatment on pro-inflammatory responses that were mediated by PaSRB2a. The pro-inflammatory responses in LPS-treated ayu were down-regulated upon PaSRB2a knockdown by lentivirus siRNA delivery. In grass carp and spotted green pufferfish, SRB2a also mediated LPS internalization and pro-inflammatory responses. Our work identifies a novel LPS signaling pathway in teleosts that differs from those in mammals, and contributes to our understanding of the evolution of pathogen recognition in vertebrates.

FAF1 Regulates Antiviral Immunity by Inhibiting MAVS but Is Antagonized by Phosphorylation upon Viral Infection

Mitochondrial antiviral signaling protein (MAVS) is an adaptor of the innate immune receptor retinoic acid-inducible gene 1 (RIG-I) that links recognition of viral RNA to antiviral signaling. Upon interacting with RIG-I, MAVS undergoes lysine 63-linked poly-ubiquitination by the E3 ligase TRIM31 and subsequently aggregates to activate downstream signaling effectors. We find that the scaffold protein FAF1 forms aggregates that negatively regulate MAVS. FAF1 antagonizes the poly-ubiquitination and aggregation of MAVS by competing with TRIM31 for MAVS association. FAF1 knockout mice are more resistant to RNA virus infection, and FAF1 deficiency in myeloid cells results in enhanced innate signaling and reduced viral load and morbidity in vivo. Upon virus infection, the kinase IKKɛ directly phosphorylates FAF1 at Ser556 and triggers FAF1 de-aggregation. Moreover, Ser556 phosphorylation promotes FAF1 lysosomal degradation, consequently relieving FAF1-dependent suppression of MAVS. These findings establish FAF1 as a modulator of MAVS and uncover mechanisms that regulate FAF1 to insure timely activation of antiviral defense.

Applications of Immunomodulatory Immune Synergies to Adjuvant Discovery and Vaccine Development

Pathogens comprise a diverse set of immunostimulatory molecules that activate the innate immune system during infection. The immune system recognizes distinct combinations of pathogenic molecules leading to multiple immune activation events that cooperate to produce enhanced immune responses, known as 'immune synergies'. Effective immune synergies are essential for the clearance of pathogens, thus inspiring novel adjuvant design to improve vaccines. We highlight current vaccine adjuvants and the importance of immune synergies to adjuvant and vaccine design. The focus is on new technologies used to study and apply immune synergies to adjuvant and vaccine development. Finally, we discuss how recent findings can be applied to the future design and characterization of synergistic adjuvants and vaccines.

CNBP controls IL-12 gene transcription and Th1 immunity

These studies reveal a previously unrecognized role for Cnbp as a novel transcriptional regulator engaged downstream of innate immune receptors controlling the c-Rel–IL-12–Th1 axis, which has important implications for both host defense and inflammatory disease.

An inducible program of inflammatory gene expression is a hallmark of antimicrobial defenses. Recently, cellular nucleic acid–binding protein (CNBP) was identified as a regulator of nuclear factor-kappaB (NF-κB)–dependent proinflammatory cytokine gene expression. Here, we generated mice lacking CNBP and found that CNBP regulates a very restricted gene signature that includes IL-12β. CNBP resides in the cytosol of macrophages and translocates to the nucleus in response to diverse microbial pathogens and pathogen-derived products. Cnbp-deficient macrophages induced canonical NF-κB/Rel signaling normally but were impaired in their ability to control the activation of c-Rel, a key driver of IL-12β gene transcription. The nuclear translocation and DNA-binding activity of c-Rel required CNBP. Lastly, Cnbp-deficient mice were more susceptible to acute toxoplasmosis associated with reduced production of IL-12β, as well as a reduced T helper type 1 (Th1) cell IFN-γ response essential to controlling parasite replication. Collectively, these findings identify CNBP as important regulator of c-Rel–dependent IL-12β gene transcription and Th1 immunity.

Polycomb chromobox Cbx2 enhances antiviral innate immunity by promoting Jmjd3-mediated demethylation of H3K27 at the Ifnb promoter

Polycomb chromobox (CBX) proteins regulate gene transcription by maintaining chromatin states, which guide a variety of biological processes. Now, epigenetic regulation of innate immune response is an emerging field. However, the role of CBX proteins in innate immunity remains unclear. We confirmed that the expression of CBX family proteins, especially Cbx2, was decreased in macrophages upon viral infection, and then we investigated the role of Cbx2 in the antiviral immune response. Silencing or knockdown of Cbx2 in macrophages inhibited virus-induced production of IFN-β. Furthermore, heterozygous Cbx2 knockout were susceptible to VSV challenge. Mechanistically, Cbx2 binds to and recruits Jmjd3 to the Ifnb promoter, leading to demethylation of H3K27me3 and increased transcription of IFN-β. Together, our study reveals a non-traditional function of a Cbx protein and adds new insight into the epigenetic regulation of antiviral innate immunity.

Melatonin suppresses TLR9-triggered proinflammatory cytokine production in macrophages by inhibiting ERK1/2 and AKT activation

Toll-like receptor (TLR) signaling plays major roles in innate immune response in macrophages. Melatonin regulates TLR3- and TLR4-mediated innate immune responses in macrophages. However, it remains unknown whether melatonin regulates TLR9-mediated innate immune responses in macrophages. Here we demonstrated that melatonin suppressed TLR9 ligand-induced proinflammatory cytokines mRNA and protein production in peritoneal macrophages without interrupting the viability of peritoneal macrophages. Using a melatonin membrane receptors MT1/MT2 antagonist luzindole, we found that MT1 and MT2 were dispensable for melatonin’s inhibitory effects on TLR9-mediated proinflammatory cytokines production, even though melatonin upregulated mRNA expression of MT1 and MT2 in macrophages. Furthermore, melatonin did not affect mRNA expressions of TLR9 and MyD88 but attenuated TLR9 ligand-induced ERK1/2 and AKT phosphorylation without affecting p38 and NF-κB p65 phosphorylation. Also, melatonin inhibited TLR9-mediated proinflammatory cytokines production in vivo. Taken together, our results demonstrate that melatonin suppresses TLR9-triggered proinflammatory cytokines production in macrophages via melatonin membrane receptor-independent manners and probably through inhibiting ERK1/2 and AKT activation, which further elucidates the roles of melatonin in regulating TLR-mediated innate immune responses in macrophages.

CD11b-activated Src signal attenuates neuroinflammatory pain by orchestrating inflammatory and anti-inflammatory cytokines in microglia

Neuroinflammation plays an important role in the induction and maintenance of chronic pain. Orchestra of pattern-recognition receptor-induced pro-inflammatory and anti-inflammatory cytokines is critical for inflammation homeostasis. CD11b on macrophages could inhibit toll-like receptor (TLR) activation-induced inflammatory responses. However, the function of CD11b on microglia remains unknown. In the current study, we demonstrated that CD11b-deficient microglia cells produced more inflammatory cytokines, such as interleukin-6 and tumor necrosis factor alpha, while less anti-inflammatory cytokines. Signal transduction assay confirmed that nuclear factor-κB activation was increased in CD11b-deficient microglia cells, which resulted from decreased activation of Src. Inhibition of Src by PP1 increased inflammation in wild-type microglia cells significantly, but not in CD11b-deficient microglia cells. In vivo, CD11b-deficient mice were more susceptible to chronic constrictive injury-induced allodynia and hyperalgesia with significantly more inflammatory cytokines expression. All these results indicated that the regulatory function of CD11b-Src signal pathway on both inflammatory and anti-inflammatory cytokines in microglia cells is a potential target in neuropathic pain treatment.

Methyltransferase Dot1l preferentially promotes innate IL-6 and IFN-β production by mediating H3K79me2/3 methylation in macrophages

Epigenetic modification, including histone modification, precisely controls target gene expression. The posttranscriptional regulation of the innate signaling-triggered production of inflammatory cytokines and type I interferons has been fully elucidated, whereas the roles of histone modification alteration and epigenetic modifiers in regulating inflammatory responses need to be further explored. Di/tri-methylation modifications of histone 3 lysine 79 (H3K79me2/3) have been shown to be associated with gene transcriptional activation. Disruptor of telomeric silencing-1-like (Dot1l) is the only known exclusive H3K79 methyltransferase and regulates the proliferation and differentiation of tumor cells. However, the roles of Dot1l and Dot1l-mediated H3K79 methylation in innate immunity and inflammatory responses remain unclear. Here, we found that H3K79me2/3 modification levels at the Il6 and Ifnb1 promoters, as well as H3K79me2 modification at the Tnfα promoter, were increased in macrophages activated by Toll-like receptor (TLR) ligands or virus infection. The innate signals upregulated Dot1l expression in macrophages and THP1 cells. Dot1l silencing or a Dot1l inhibitor preferentially suppressed the production of IL-6 and interferon (IFN)-β but not of TNF-α in macrophages and THP1 cells triggered by TLR ligands or virus infection. Dot1l was recruited to the proximal promoter of the Il6 and Ifnb1 but not Tnfα gene and then mediated H3K79me2/3 modification at the Il6 and Ifnb1 promoters, consequently facilitating the transcription and expression of Il6 and Ifnb1. Thus, Dot1l-mediated selective H3K79me2/3 modifications at the Il6 and Ifnb1 promoters are required for the full activation of innate immune responses. This finding adds new insights into the epigenetic regulation of inflammatory responses and pathogenesis of autoimmune diseases.

Self-associated molecular patterns mediate cancer immune evasion by engaging Siglecs on T cells

First-generation immune checkpoint inhibitors, including anti-CTLA-4 and anti-programmed death 1 (anti-PD-1) antibodies, have led to major clinical progress, yet resistance frequently leads to treatment failure. Thus, new targets acting on T cells are needed. CD33-related sialic acid-binding immunoglobulin-like lectins (Siglecs) are pattern-recognition immune receptors binding to a range of sialoglycan ligands, which appear to function as self-associated molecular patterns (SAMPs) that suppress autoimmune responses. Siglecs are expressed at very low levels on normal T cells, and these receptors were not until recently considered as interesting targets on T cells for cancer immunotherapy. Here, we show an upregulation of Siglecs, including Siglec-9, on tumor-infiltrating T cells from non-small cell lung cancer (NSCLC), colorectal, and ovarian cancer patients. Siglec-9-expressing T cells coexpressed several inhibitory receptors, including PD-1. Targeting of the sialoglycan-SAMP/Siglec pathway in vitro and in vivo resulted in increased anticancer immunity. T cell expression of Siglec-9 in NSCLC patients correlated with reduced survival, and Siglec-9 polymorphisms showed association with the risk of developing lung and colorectal cancer. Our data identify the sialoglycan-SAMP/Siglec pathway as a potential target for improving T cell activation for immunotherapy.

Reshaping of the Dendritic Cell Chromatin Landscape and Interferon Pathways during HIV Infection

Myeloid dendritic cells (DCs) have the innate capacity to sense pathogens and orchestrate immune responses. However, DCs do not mount efficient immune responses to HIV-1, primarily due to restriction of virus reverse transcription, which prevents accumulation of viral cDNA and limits its detection through the cGAS-STING pathway. By allowing reverse transcription to proceed, we find that DCs detect HIV-1 in distinct phases, before and after virus integration. Blocking integration suppresses, but does not abolish, activation of the transcription factor IRF3, downstream interferon (IFN) responses, and DC maturation. Consistent with two stages of detection, HIV-1 "primes" chromatin accessibility of innate immune genes before and after integration. Once primed, robust IFN responses can be unmasked by agonists of the innate adaptor protein, MyD88, through a process that requires cGAS, STING, IRF3, and nuclear factor κB. Thus, HIV-1 replication increases material available for sensing, and discrete inflammatory inputs tune cGAS signaling to drive DC maturation.

Integrating the DNA damage and protein stress responses during cancer development and treatment

During evolution, cells have developed a wide spectrum of stress response modules to ensure homeostasis. The genome and proteome damage response pathways constitute the pillars of this interwoven 'defensive' network. Consequently, the deregulation of these pathways correlates with ageing and various pathophysiological states, including cancer. In the present review, we highlight: (1) the structure of the genome and proteome damage response pathways; (2) their functional crosstalk; and (3) the conditions under which they predispose to cancer. Within this context, we emphasize the role of oncogene-induced DNA damage as a driving force that shapes the cellular landscape for the emergence of the various hallmarks of cancer. We also discuss potential means to exploit key cancer-related alterations of the genome and proteome damage response pathways in order to develop novel efficient therapeutic modalities. © 2018 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Extracellular DNA and autoimmune diseases

Extracellular DNA is secreted from various sources including apoptotic cells, NETotic neutrophils and bacterial biofilms. Extracellular DNA can stimulate innate immune responses to induce type-I IFN production after being endocytosed. This process is central in antiviral responses but it also plays important role in the pathogenesis of a range of autoimmune diseases such as systemic lupus erythematosus. We discuss the recent advances in the understanding of the role of extracellular DNA, released from apoptotic and NETotic cells, in autoimmunity.

Chaihu-Shugan-San Decoction Modulates Intestinal Microbe Dysbiosis and Alleviates Chronic Metabolic Inflammation in NAFLD Rats via the NLRP3 Inflammasome Pathway

We evaluate the effects of the Chaihu-Shugan-San decoction on intestinal microbe dysbiosis and chronic metabolic inflammation via the NLRP3 pathway in NAFLD rats that were fed a high-fat diet. Twenty-four SD rats (male, six weeks old, 200 ± 20 g) were randomly divided into three groups: normal control group (NC group), high-fat diet-fed group (HFD group), and Chaihu-Shugan-San decoction intervention group (CH group). The NC group rats were given standard feed, the HFD group rats were all fed a high-fat diet (83% standard feed + 10% lard oil + 5% sucrose + 1.5% cholesterol + 0.5% cholate), and the CH group rats were given a HFD plus Chaihu-Shugan-San at 9.6 g•kg-1•d-1. Body composition, serum and liver lipids, inflammatory markers, intestinal microbial population, and the NLRP3 pathway-associated protein were assessed. The results showed that Chaihu-Shugan-San decoction significantly reduced body weight and total fat mass and the levels of serum LPS, TG, TNF-α, IL-1β, and IL-18, as well as liver TC, TG, TNF-α, IL-1β, and IL-18 (P < 0.05). The abundance of Enterobacteriaceae (0.375% versus 0.064%, P < 0.05), Staphylococcaceae families (0.049% versus 0.016%, P < 0.05) and Veillonella genus (0.096% versus 0.009%, P < 0.01) significantly decreased, whereas the abundance of Anaeroplasma genus (0.0005% versus 0.0178%, P < 0.01) significantly increased. The expression levels of NLRP3, ASC, and Caspase-1 were changed significantly (P < 0.05). In summary, the Chaihu-Shugan-San decoction modulated intestinal microbe dysbiosis, reduced fat accumulation, and alleviated inflammatory factor expression, which are all processes related to the NLRP3 inflammasome pathway in NAFLD rats.

UntRIG(er)ing lncRNAs

In a recent Cell paper, Jiang et al. (2018) have shown that lnc-Lsm3b, a long non-coding RNA induced by type I IFN late in the infection in mouse macrophages, prevents further activation of RIG-I acting as a decoy for RIG-I.

The methyltransferase PRMT6 attenuates antiviral innate immunity by blocking TBK1-IRF3 signaling

Protein arginine methyltransferases (PRMTs) play diverse biological roles and are specifically involved in immune cell development and inflammation. However, their role in antiviral innate immunity has not been elucidated. Viral infection triggers the TBK1-IRF3 signaling pathway to stimulate the production of type-I interferon, which mediates antiviral immunity. We performed a functional screen of the nine mammalian PRMTs for regulators of IFN-β expression and found that PRMT6 inhibits the antiviral innate immune response. Viral infection also upregulated PRMT6 protein levels. We generated PRMT6-deficient mice and found that they exhibited enhanced antiviral innate immunity. PRMT6 deficiency promoted the TBK1-IRF3 interaction and subsequently enhanced IRF3 activation and type-I interferon production. Mechanistically, viral infection enhanced the binding of PRMT6 to IRF3 and inhibited the interaction between IRF3 and TBK1; this mechanism was independent of PRMT6 methyltransferase activity. Thus, PRMT6 inhibits antiviral innate immunity by sequestering IRF3, thereby blocking TBK1-IRF3 signaling. Our work demonstrates a methyltransferase-independent role for PRMTs. It also identifies a negative regulator of the antiviral immune response, which may protect the host from the damaging effects of an overactive immune system and/or be exploited by viruses to escape immune detection.

Advances and Opportunities in Nanoparticle- and Nanomaterial-Based Vaccines against Bacterial Infections

As the dawn of the postantibiotic era we approach, antibacterial vaccines are becoming increasingly important for managing bacterial infection and reducing the need for antibiotics. Despite the success of vaccination, vaccines remain unavailable for many pressing microbial diseases, including tuberculosis, chlamydia, and staphylococcus infections. Amid continuing research efforts in antibacterial vaccine development, the advancement of nanomaterial engineering has brought forth new opportunities in vaccine designs. With increasing knowledge in antibacterial immunity and immunologic adjuvants, innovative nanoparticles are designed to elicit the appropriate immune responses for effective antimicrobial defense. Rationally designed nanoparticles are demonstrated to overcome delivery barriers to shape the adaptive immunity. This article reviews the advances in nanoparticle- and nanomaterial-based antibacterial vaccines and summarizes the development of nanoparticulate adjuvants for immune potentiation against microbial pathogens. In addition, challenges and progress in ongoing antibacterial vaccine development are discussed to highlight the opportunities for future vaccine designs.

TRIM21 Promotes Innate Immune Response to RNA Viral Infection through Lys27-Linked Polyubiquitination of MAVS

Human innate immunity responds to viral infection by activating the production of interferons (IFNs) and proinflammatory cytokines. The mitochondrial adaptor molecule MAVS plays a critical role in innate immune response to viral infection. In this study, we show that TRIM21 (tripartite motif-containing protein 21) interacts with MAVS to positively regulate innate immunity. Under viral infection, TRIM21 is upregulated through the IFN/JAK/STAT signaling pathway. Knockdown of TRIM21 dramatically impairs innate immune response to viral infection. Moreover, TRIM21 interacts with MAVS and catalyzes its K27-linked polyubiquitination, thereby promoting the recruitment of TBK1 to MAVS. Specifically, the PRY-SPRY domain of TRIM21 is the key domain for its interaction with MAVS, while the RING domain of TRIM21 facilitates the polyubiquitination chains of MAVS. In addition, the MAVS-mediated innate immune response is enhanced by both the PRY-SPRY and RING domains of TRIM21. Mutation analyses of all the lysine residues of MAVS further revealed that Lys325 of MAVS is catalyzed by TRIM21 for the K27-linked polyubiquitination. Overall, this study reveals a novel mechanism by which TRIM21 promotes the K27-linked polyubiquitination of MAVS to positively regulate innate immune response, thereby inhibiting viral infection.IMPORTANCE Activation of innate immunity is essential for host cells to restrict the spread of invading viruses and other pathogens. MAVS plays a critical role in innate immune response to RNA viral infection. In this study, we demonstrated that TRIM21 targets MAVS to positively regulate innate immunity. Notably, TRIM21 targets and catalyzes K27-linked polyubiquitination of MAVS and then promotes the recruitment of TBK1 to MAVS, leading to upregulation of innate immunity. Our study outlines a novel mechanism by which the IFN signaling pathway blocks RNA virus to escape immune elimination.

The E3 Ubiquitin Ligase TRIM40 Attenuates Antiviral Immune Responses by Targeting MDA5 and RIG-I

Retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs), including melanoma differentiation-associated gene 5 (MDA5) and RIG-I, are crucial for host recognition of non-self RNAs, especially viral RNA. Thus, the expression and activation of RLRs play fundamental roles in eliminating the invading RNA viruses and maintaining immune homeostasis. However, how RLR expression is tightly regulated remains to be further investigated. In this study, we identified a major histocompatibility complex (MHC)-encoded gene, tripartite interaction motif 40 (TRIM40), as a suppressor of RLR signaling by directly targeting MDA5 and RIG-I. TRIM40 binds to MDA5 and RIG-I and promotes their K27- and K48-linked polyubiquitination via its E3 ligase activity, leading to their proteasomal degradation. TRIM40 deficiency enhances RLR-triggered signaling. Consequently, TRIM40 deficiency greatly enhances antiviral immune responses and decreases viral replication in vivo. Thus, we demonstrate that TRIM40 limits RLR-triggered innate activation, suggesting TRIM40 as a potential therapeutic target for the control of viral infection.

Ca2+/Calmodulin-Dependent AtSR1/CAMTA3 Plays Critical Roles in Balancing Plant Growth and Immunity

During plant-pathogen interactions, plants have to relocate their resources including energy to defend invading organisms; as a result, plant growth and development are usually reduced. Arabidopsis signal responsive1 (AtSR1) has been documented as a negative regulator of plant immune responses and could serve as a positive regulator of plant growth and development. However, the mechanism by which AtSR1 balances plant growth and immunity is poorly understood. Here, we performed a global gene expression profiling using Affymetrix microarrays to study how AtSR1 regulates defense- and growth-related genes in plants with and without bacterial pathogen infection. Results revealed that AtSR1 negatively regulates most of the immune-related genes involved in molecular pattern-triggered immunity (PTI), effector-triggered immunity (ETI), and in salicylic acid (SA)- and jasmonate (JA)-mediated signaling pathways. AtSR1 may rigidly regulate several steps of the SA-mediated pathway, from the activation of SA synthesis to the perception of SA signal. Furthermore, AtSR1 may also regulate plant growth through its involvement in regulating auxin- and BRs-related pathways. Although microarray data revealed that expression levels of defense-related genes induced by pathogens are higher in wild-type (WT) plants than that in atsr1 mutant plants, WT plants are more susceptible to the infection of virulent pathogen as compared to atsr1 mutant plants. These observations indicate that the AtSR1 functions in suppressing the expression of genes induced by pathogen attack and contributes to the rapid establishment of resistance in WT background. Results of electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation (ChIP)-PCR assays suggest that AtSR1 acts as transcription factor in balancing plant growth and immunity, through interaction with the “CGCG” containing CG-box in the promotors of its target genes.

The cGas-Sting Signaling Pathway Is Required for the Innate Immune Response Against Ectromelia Virus

Activation of the DNA-dependent innate immune pathway plays a pivotal role in the host defense against poxvirus. Cyclic GMP-AMP synthase (cGAS) is a key cytosolic DNA sensor that produces the cyclic dinucleotide cGMP-AMP (cGAMP) upon activation, which triggers stimulator of interferon genes (STING), leading to type I Interferons (IFNs) production and an antiviral response. Ectromelia virus (ECTV) has emerged as a valuable model for investigating the host-Orthopoxvirus relationship. However, the role of cGas-Sting pathway in response to ECTV is not clearly understood. Here, we showed that murine cells (L929 and RAW264.7) mount type I IFN responses to ECTV that are dependent upon cGas, Sting, TANK binding kinase 1 (Tbk1), and interferon regulatory factor 3 (Irf3) signaling. Disruption of cGas or Sting expression in mouse macrophages blocked the type I IFN production and facilitated ECTV replication. Consistently, mice deficient in cGas or Sting exhibited lower type I IFN levels and higher viral loads, and are more susceptible to mousepox. Collectively, our study indicates that the cGas-Sting pathway is critical for sensing of ECTV infection, inducing the type I IFN production, and controlling ECTV replication.

Condensin Smc4 promotes inflammatory innate immune response by epigenetically enhancing NEMO transcription

Structural maintenance of chromosome (Smc) protein complex (condensin) plays a central role in organizing and compacting chromosomes, which determines DNA-binding activity and gene expression; however, the role of condensin Smc in innate immunity and inflammation remains largely unknown. Through a high-throughput screening of the epigenetic modifiers, we identified Smc4, a core subunit of condensin, to potentially promote inflammatory innate immune response. Knockdown or deficiency of Smc4 inhibited TLR- or virus-triggered production of proinflammatory cytokines IL-6, TNF-α and IFN-β in macrophages. Mice with Smc4 knockdown were less susceptible to sepsis. Mechanistically, Smc4 enhanced NEMO transcription by recruiting H4K5ac to and increasing H4K5 acetylation of nemo promoter, leading to innate signals-triggered more potent activation of NF-κB and IRF3 pathways. Therefore, Smc4 promotes inflammatory innate immune responses by enhancing NEMO transcription, and our data add insight to epigenetic regulation of innate immunity and inflammation, and outline potential target for controlling inflammatory diseases.

Integration of danger peptide signals with herbivore-associated molecular pattern signaling amplifies anti-herbivore defense responses in rice

Plant defense against herbivores is modulated by herbivore-associated molecular patterns (HAMPs) from oral secretions (OS) and/or saliva of insects. Furthermore, feeding wounds initiate plant self-damage responses modulated by danger-associated molecular patterns (DAMPs) such as immune defense-promoting plant elicitor peptides (Peps). While temporal and spatial co-existence of both patterns during herbivory implies a possibility of their close interaction, the molecular mechanisms remain undetermined. Here we report that exogenous application of rice (Oryza sativa) peptides (OsPeps) can elicit multiple defense responses in rice cell cultures. Specific activation of OsPROPEP3 gene transcripts in rice leaves by wounding and OS treatments further suggests a possible involvement of the OsPep3 peptide in rice-herbivore interactions. Correspondingly, we found that simultaneous application of OsPep3 and Mythimna loreyi OS significantly amplifies an array of defense responses in rice cells, including mitogen-activated protein kinase activation, and generation of defense-related hormones and metabolites. The induction of OsPROPEP3/4 by OsPep3 points to a positive auto-feedback loop in OsPep signaling which may contribute to additional enhancement of defense signal(s). Finally, the overexpression of the OsPep receptor OsPEPR1 increases the sensitivity of rice plants not only to the cognate OsPeps but also to OS signals. Our findings collectively suggest that HAMP-DAMP signal integration provides a critical step in the amplification of defense signaling in plants.

The interferon-stimulated gene TRIM22: A double-edged sword in HIV-1 infection

Infection of target cells by the human immunodeficiency virus type-1 (HIV-1) is hampered by constitutively expressed host cell proteins preventing or curtailing virus replication and therefore defined as "restriction factors". Among them, members of the tripartite motif (TRIM) family have emerged as important players endowed with both antiviral effects and modulatory capacity of the innate immune response. TRIM5α and TRIM19 (i.e. promyelocytic leukemia, PML) are among the best-characterized family members; however, in this review we will focus on the potential role of another family member, i.e. TRIM22, a factor strongly induced by interferon stimulation, in HIV infection in vivo and in vitro in the context of its broader antiviral effects. We will also focus on the potential role of TRIM22 in HIV-1-infected individuals speculating on its dual role in controlling virus replication and more complex role in chronic infection. At the molecular levels, we will review the evidence in favor of a relevant role of TRIM22 as epigenetic inhibitor of HIV-1 transcription acting by preventing the binding of the host cell transcription factor Sp1 to the viral promoter. These evidences suggest that TRIM22 should be considered a potential new player in either the establishment or maintenance of HIV-1 reservoirs of latently infected cells unaffected by combination antiretroviral therapy.

MLL5 suppresses antiviral innate immune response by facilitating STUB1-mediated RIG-I degradation

Trithorax group protein MLL5 is an important epigenetic modifier that controls cell cycle progression, chromatin architecture maintenance, and hematopoiesis. However, whether MLL5 has a role in innate antiviral immunity is largely unknown. Here we show that MLL5 suppresses the RIG-I-mediated anti-viral immune response. Mll5-deficient mice infected with vesicular stomatitis virus show enhanced anti-viral innate immunity, reduced morbidity, and viral load. Mechanistically, a fraction of MLL5 located in the cytoplasm interacts with both RIG-I and its E3 ubiquitin ligase STUB1, which promotes K48-linked polyubiquitination and proteasomal degradation of RIG-I. MLL5 deficiency attenuates the RIG-I and STUB1 association, reducing K48-linked polyubiquitination and accumulation of RIG-I protein in cells. Upon virus infection, nuclear MLL5 protein translocates from the nucleus to the cytoplasm inducing STUB1-mediated degradation of RIG-I. Our study uncovers a previously unrecognized role for MLL5 in antiviral innate immune responses and suggests a new target for controlling viral infection.

MLL5 is an essential epigenetic modifier involved in cell cycle progression, chromatin architecture and hematopoiesis. Here the authors establish that MLL5 suppresses the innate immune response in a murine model of virus infection by targeting and promoting degradation of RIG-I.